1. Field of the Invention
The present invention relates to a process for manufacturing transparent or translucent heavy duty liquid laundry detergent compositions containing polymer or polymers (e.g., polymer gums) capable of suspending relatively large size particles while remaining readily pourable (good shear thinning properties). The suspended particles generally comprise a component subject to degradation (e.g., encapsulated enzyme and/or bleach) and/or a component not soluble in heavy duty liquid and which causes an opaque appearance. Through careful selection of polymer/polymers, it is possible to find a polymer suspending system stable in ionic (e.g., high surfactant) environment and which simultaneously provides consumer desirable appearance. Through unique processing of polymer(s), the above-noted properties can be achieved. In particular, the present invention is concerned with formation of a non-continuous network suspending system.
2. Background
For a variety of reasons, it is often greatly desirable to suspend particles in heavy duty liquid detergent compositions. For example, because there are certain components (e.g., bleaches, enzymes, perfumes) which readily degrade in the hostile environment of surfactant containing heavy duty liquids, these components can be protected in capsule particles (such as described, for example, in U.S. Pat. Nos. 5,281,355 and 5,281,356 both to Tsaur et al., hereby incorporated by reference into the subject application) and the capsule particles may be suspended in the heavy duty liquid detergents. Other particles which may be suspended include enzymes (whether or not encapsulated) and other desirable ingredients (e.g., aminosilicone oil, PVP, soil release agents, anti-redeposition agents, antiwrinkle agents etc.)
One way to suspend particles in liquid compositions is to use so-called "structured" heavy duty liquids (sometimes referred to in the art as "duotropic" liquids and in contrast to single continuous phase "isotropic" liquids). Structured liquids may be broadly characterized in that they contain high levels of electrolyte and in that the liquids form so-called lamellar layers which are like sheets or plates in close proximity to one other. Structured liquids are well defined in U.S. Pat. No. 5,147,576 to Montague et al., hereby incorporated by reference into the subject application. Such structured liquids, by virtue of their close packing and lamellar sheets, are generally able to suspend particles (e.g., capsules, enzymes, polymers) more readily than isotropic liquids. Structured liquids are often difficult to pour and, because they are lamellar, are generally, if not always, opaque.
Another way of suspending particles in liquids is through the use of certain structuring gums (e.g., xanthan gum, rhamsan gum and the like). While such gums are desirably used to structure liquids and suspend particles, however, they are notoriously susceptible to electrolytes (e.g., surfactants) present in the compositions and so may generally only be used when the level of surfactant is severely limited (e.g., less than 10% by wt.). By contrast, compositions of the present invention comprise greater than 15%, preferably greater than 17% most preferably 20-85% by wt. surfactant. Use of polymer gums and such levels of surfactant is known to lead to instability precipitation which in turn leads to non-clear product and phase separation.
Moreover, when used to thicken compositions, the gum polymers are generally used in such high amounts as to render the compositions very difficult to pour. By difficult to pour is meant less than about 3000 cps at 21S.sup.-1 shear rate measured at room temperature (measurements of invention were made using Haake RV20 Rotovisco RC20 Rheocontroller; preferred sensor systems were MV1, MV2 and MV3 sensor systems).
As far as applicants are aware, all attempts to suspend particles, particularly large size particles (e.g., 300 to 5000 microns, preferably 500 or greater to 3000 microns), in liquid compositions, particularly those containing greater than 15% surfactant, while maintaining processability have been unsuccessful.
U.S. Pat. No. 4,749,512 to Brown et al., for example, teaches suspension of builder salts in automatic dishwashing formulations. The compositions are neither translucent nor transparent. The compositions also contain no water and no polymeric thickeners. The builders are suspended due to surfactant structuring.
U.S. Pat. No. 5,562,939 to Lewis teaches a method using a pre-gel process to suspend particles in liquid. The compositions have no surfactant and a pH of 2.5 to 6, preferably 3.0 compared to much higher surfactant levels and pH (about 6 to 13, preferably 8 to 10) of the subject invention.
U.S. Pat. No. 5,597,790 to Thoen teaches suspension of solid peroxygen compounds having particle size of 0.5 to 20 microns in liquid detergents using low levels of silicate. The suspended particles were much smaller than those of the invention.
Finally GB 1,303,810 discloses clear liquid medium and a visually distinct component of at least 0.5 millemeter particle size. However where more than 10% surfactant is used, only clays, not gums are used to structure. Where a gum is used to structure (Kelzan), no more than 10% surfactant is used.
In short, there is no teaching in the art of heavy duty liquid compositions containing 15% or greater, preferably about 20% to 85% surfactant, more preferably 21% to 75% comprising suspending gum polymers stable in high surfactant environment (e.g., don't phase separate and cause opaqueness) able to suspend large size particles and simultaneously provide translucent/transparent, pourable compositions.
While not wishing to be bound by theory, it is believed these compositions can be formed only because of applicants realization that the suspending polymers (e.g., gums) must be given sufficient time or heat to swell, preferably while not in the presence of surfactant or electrolyte (e.g., surfactant or electrolyte may compete for water preventing water gain by the gum).
The swollen polymer/gum (wherein degree of swelling may be measured using in indicators or other techniques known to those skilled in the art) can then be formed into "suspension bits" by agitation of polymer gum solution in combination with a chemical or mechanical means selected from the group consisting of addition of counterion (e.g., causing polymer gum aggregation); temperature effect (e.g., temperature causing change in polymer gum); or mixtures thereof. Detergent base may be separately formed and added to pre-formed "bits" to form a "non-continuous" aggregation of gum particles sufficient to form a suspending network; or surfactant and other final detergent component may be added to a polymer gum solution to form suspending particles in situ. Although this in situ method may comprise addition of counterion to form "bits" while surfactant is being slowly added, depending on gum selection, it is possible to practice this method with no counterion addition as well.
In any event, because a pre-swollen polymer gum solution is first formed without surfactant competition (e.g., for water), surprisingly and unexpectedly it has been found possible to form a transparent/translucent liquid detergent system which suspends large size particles and is readily pourable. Moreover, the suspending polymer gums are not susceptible to ionic agents and/or surfactants and can form these transparent particle suspending function in a high surfactant environment without precipitating to form opaque depositions or phase separate. This is completely novel to the art as far as applicants are aware.
The subject invention is directed to selection of specific gums and formation of non-continuous network suspending system while a companion case is directed to selection of specific gums to form a "continuous" suspending network.